Soil-borne pathogenic fungi cause damping off, root-rot, crown-rot and neck-rot in a wide variety of seedling crops. Among these pathogenic fungi are fungi of the genera Rhizoctonia, Pythium, Sclerotium, Phytophotora and Fusarium. These fungi are capable of attacking and causing extensive damage to many common and commercially important crops, such as beans, tomatoes, cotton, peanuts, potatoes, lettuce, ornamental flowers and others.
Chemical fungicides have been widely used to control these soil-borne pathogens. The use of such chemicals is expensive and may result in ecological damage and in the increased incidence of occupational diseases. A promising alternative to such chemical control is the biological control of soil plant pathogens by naturally-occurring microorganisms. These biological control agents may be used alone or in conjunction with lesser amounts of chemical fungicides.
The use of antagonistic microorganisms in controlling plant pathogenic fungi has been the subject of extensive research. A large part of this research has been concerned with myco parasitism, the parasitism by one fungus of another. One of the most frequently studied mycoparasites in relation to biological control is the genus Trichoderma. (Y. Elad et al., 1982, Can. J. Microbiol. 28: 719-725, I. Chet and R. Baker, 1981, Phytopathology 71: 286-290; M. N. Schroth and J. G. Hancock, 1981, Ann. Rev. Microbiology 35: 459-463; Y. Elad, et al., 1981, Plant Disease 65:675-677; Y. Elad, et al., 1980, Phytopathology 70: 119-121; I. Chet et al., 1979, in B. Scippers and W. Gams. eds, "Soil Borne Plant Pathogens", Academic Press, NY, NY; Y. Hadar et al., 1979, Phytopathology 69:64-68; C. Dennis and J. Webster, 1971, Trans. Br. mycol. Soc. 57(3), 363-369).
Species or strains of Trichoderma may be differentially antagonistic to different species of fungi. (H. D. Wells et al., 1972, Phytopathology 62:442-447). Such differences in antagonism have been found both within and between species of Trichoderma (D. K. Bell et al., 1982, Phytopathology 72:379-382).
In addition to such differences in antagonism, it has been determined that the environment in which the interaction occurs also affects the degree of biological control. Antagonism in culture is often not reproducible in the complex environment present in the soil under greenhouse or field conditions. (M. N. Schroth and J. G. Hancock, 1981, Ann. Rev. Microbiol. 35:453-76). As a result, tests made under non-soil culture conditions are not truly indicative of the potential for use of the Trichoderma isolate as a biological control agent.
Due to the significant differences in antogonism of Trichoderma isolates to various pathogens under different environmental conditions, researchers have concentrated their efforts on searching for Trichoderma antagonists against specific disease causing plant pathogenic fungi. The likelihood of finding a specific biological antagonist with a wide range of antagonism under field conditions to several species of plant pathogens was considered remote. (D. K. Bell et al., 1982, Phytopathology 72:379-382).